Multi-layer sheet

ABSTRACT

A multi-layer sheet which has a follow-up layer being composed of a resin composition containing a resin having a melting point, which is the melting peak temperature measured by DSC, in the range of 50 to 130° C. as a primary component, and a releasing layer being composed of a resin composition containing a resin having a melting point of 200° C. or higher as a primary component and being laminated on the above follow-up layer, wherein when the two releasing layers of the above multi-layer sheets are closely contacted with each other under a condition of 170° C. and 3 MPa for 30 minutes, they exhibit a blocking force of 0.1 N/cm or less as measured in accordance with ASTM D1893. The multi-layer sheet is excellent in heat resistance, releasing characteristics and follow-up characteristics to an irregular surface, exhibits excellent non-staining characteristics and also can be easily disposed of after use.

TECHNICAL FIELD

The present invention relates to a multi-layer sheet which is excellentin heat resistance, releasability and staining resistance and/orexcellent in following-up property to an irregular surface, and can alsobe easily disposed of after the sheet is used.

BACKGROUND ART

In the process for producing a printed circuit board, a flexible printedcircuit board, a multi-layer printed circuit board or the like, areleasing sheet is used at the time of hot-pressing a copper-cladlaminated sheet or a copper foil through an interposed prepreg or heatresistant film is interposed. In the process for producing a flexibleprinted board, at the time of hot-pressing and bonding a cover-lay filmonto the body of the flexible printed board, wherein electric circuitsare formed, with a thermosetting adhesive agent, the method using areleasing sheet is widely performed in order to prevent the cover-layfilm from being bonded to the press hot plate.

The releasing sheet is required to follow up irregularities in thesurface of a board. In the case that the sheet is used to produce aflexible printed board, the sheet is required to prevent a matter that athermosetting adhesive agent is forced out from between a cover-lay filmand the body of the flexible board, thereby staining the board.

Meanwhile, Japanese Patent Application Laid-Open No. 2-175247 disclosesa releasing sheet made of a laminate wherein a soft polyolefin layer isused as an intermediate layer and crystalline polymethylpentene layersare formed on its inside and outside faces. Japanese Patent ApplicationLaid-Open No. 2-24139 discloses a releasing multi-layer film for a printcircuit laminating step wherein an intermediate layer is made of acopolymer resin made from ethylene and methyl methacrylate and upper andlower layers, between which the intermediate layer is sandwiched, aremade of polypropylene or polymethylpentene. These releasing sheets areeach a sheet wherein an intermediate layer made of a resin having a lowsoftening resin is sandwiched between layers excellent in releasability,thereby making its following-up property to a board surface and itsreleasability compatible with each other.

However, these releasing sheets have a problem that the resin whichconstitutes the intermediate layer, the softening temperature of theresin being low, is forced out at the time of hot-press so that theresin stains the board or press hot plate. On the other hand,polymethylpentene or polypropylene used as a releasing layer isexcellent in releasability but has a problem that at the time of hotpress the resin or low molecular weight products originating fromadditives contained therein are shifted to the board so as to stain, inparticular, circuits thereon, which is made of copper or the like andthus it is feared that the quality thereof is unsatisfactory forinstruments used in the field of communication, for which a high qualityis required, or others.

Hitherto, a fluorine-containing sheet as disclosed in, for example,Japanese Patent Application Laid-Open No. 5-283862 has also been used asa sheet excellent in releasability in many cases. However, thefluorine-containing sheet is expensive and further has problems that thesheet is not easily burned up and generates poisonous gas in wasteincinerating disposal after the use of the sheet although the sheet isexcellent in heat resistance, releasability and stain resistance. Thus,the sheet does not sufficiently meet social requests about environmentalproblems and safety.

Japanese Patent Application Laid-Open No. 1-229045 discloses a releasingsheet wherein stain resistance is improved by applying a mixture of ahigher alcohol or the like, a zirconium compound and a titanium compoundonto a surface of a polyester sheet. However, even if such a surfacetreatment is conducted, the resistance thereof against stains onto apartner member is not yet sufficient under conditions for hot press orthe like.

Meanwhile, Japanese Patent No. 2659404 discloses a multi-layer film, forreleasing, wherein an intermediate layer is made of a copolymer resinmade from ethylene and methyl methacrylate and resin layers made ofpolypropylene or polymethylpentene are laminated on and beneath theintermediate layer. This releasing multi-layer film is used as areleasing film when a flexible printed circuit board is produced. It isstated therein that the shape-following-up property thereof is made highby use of the copolymer resin composition comprising ethylene and methylmethacrylate as the intermediate layer and further the releasabilitythereof are made high since the layers on both sides is made ofpolypropylene or polymethylpentene. It is also stated that theabove-mentioned adhesive agent exudation gets less in hot press at thetime of producing a printed circuit board.

Similarly, Japanese Patent Application Laid-Open No. 2003-246019discloses a releasing film used in a method for producing a flexiblewiring board. In this releasing film, the following are laminated: areleasing layer made of polymethylpentene or a copolymer ofpolymethylpentene and an α-olefin and a releasing opposite-side layermade of a copolymer selected from an α-olefin copolymer, an acrylic acidester copolymer and other copolymers. The melt flow rate of the resin ofthe releasing opposite-side layer and the melting point thereof are setinto the range of 0.3 to 10.0 g/L and that of 50 to 150° C.,respectively, and the Rockwell hardness of the resin constituting thereleasing layer and the thickness thereof are set into the range of 65to 88 and that of 10 to 100 μm, respectively. The film further has astructure wherein an adhesive resin layer is interposed between thereleasing layer and the releasing opposite-side layer. About thisreleasing film also, it is stated that when this film is used as areleasing film in the process for producing a flexible printed circuitboard, the releasability and shape-following-up property are made high.

However, according to the structures described in Japanese Patent No.2659404 and Japanese Patent Application Laid-Open No. 2003-246019, theshape-following-up property is not yet sufficient in the case of usingthe structure as a releasing sheet when many flexible printed boards arelaminated and then the resultant is hot-pressed at a time by a hot pressmethod. For this reason, there is a problem that, for example, in aflexible printed circuit board, an adhesive agent is forced out ontoelectrode lands which are electrode portions made of Cu or the like andare made naked for electric connection to the outside so that thereliability of the electric connection is damaged.

Patent document 1: Japanese Patent Application Laid-Open No. 2-175247

Patent document 2: Japanese Patent Application Laid-Open No. 2-24139

Patent document 3: Japanese Patent Application Laid-Open No. 5-283862

Patent document 4: Japanese Patent Application Laid-Open No. 1-229045

Patent document 5: Japanese Patent No. 2659404

Patent document 6: Japanese Patent Application Laid-Open No. 2003-246019

DISCLOSURE OF THE INVENTION

In light of the above-mentioned present situation, an object of thepresent invention is to provide a multi-layer sheet which is excellentin heat resistance, releasability and staining resistance, and can alsobe easily disposed of after the sheet is used.

Another object of the present invention is to provide a multi-layersheet which is excellent in following-up property to an irregularsurface, is excellent in resistance against the forcing-out of theconstituents thereof, and can also be easily disposed of after the sheetis used.

According to a broad aspect of the present invention, provided is amulti-layer sheet which has a following-up layer comprising a resincomposition including mainly a resin having a melting point, which ismelting peak temperature measured by DSC, in the range of 50 to 130° C.,and a releasing layer comprising a resin composition including mainly aresin having a melting point of 200° C. or higher and laminated on thefollowing-up layer, wherein when the two releasing layers of of themulti-layer sheets are pressed and bonded onto each other under acondition of 170° C. and 3 MPa for 30 minutes, the releasing layersexhibit a blocking force of 0.1 N/cm or less, the blocking force beingmeasured in accordance with ASTM D1893.

In a specific aspect of the multi-layer sheet according to the presentinvention, at the time of calling the resin having a melting point inthe range of 50 to 130° C. a first resin, the following-up layer furthercomprises a second resin having a melting point higher than 130° C. andnot higher than 250° C. besides the first resin.

In another specific aspect of the multi-layer sheet according to thepresent invention, the following-up layer has a complex viscosity of1000 to 10000 Pa·s at 170° C. and a tan δ of less than 1 at 170° C.

In the invention, the multi-layer sheet may have various laminatestructures as long as the following-up layer and the releasing layer arelaminated on each other. For example, a second releasing layer may belaminated on a face of the following-up layer which is opposite to thefollowing-up layer face on which the releasing layer is laminated. Inthis case, the second releasing layer comprises a resin compositionincluding mainly a resin having a melting point of 200° C. or higher.

In the present invention, a sheet means not only a sheet but also afilm. The present invention will be described in detail hereinafter.

The multi-layer sheet of the present invention has at least afollowing-up layer and a releasing layer. The following-up layer is alayer for securing following-up property to irregularities in a boardsurface, and the releasing layer is a layer for securing releasabilityfrom a board or press hot plate. The following-up layer whichconstitutes the multi-layer sheet of the invention is made mainly of atleast one resin having a melting point of 50 to 130° C. In the case ofcalling this resin, which has a melting point of 50 to 130° C., a firstresin, the following-up layer preferably comprises a second resin havinga melting point higher than 130° C. and not higher than 250° C. besidesthe first resin. The first and second resins each need to have a meltingpoint of 250° C. or lower. The melting point of the first resin is inthe range of 50 to 130° C. and that of the second resin is higher than130° C. and not higher than 250° C. In the instant specification, themelting point of a resin means the melting peak temperature of the resinmeasured by DSC.

If the melting points of the first and second resins in the following-uplayer are higher than 250° C. in the invention, the shape-following-upproperty of the following-up layer cannot be made higher than that ofthe releasing layer. When the melting point of the first resin, which isone of the resins, is from 50 to 130° C. and the melting point of thesecond resin is set to higher than 130° C., the first resin secures asufficient shape-following-up property and the second resin restrainsthe resins from being forced out at the time of hot press. If at leastone of the resins is not in the range of 50 to 130° C., a sufficientshape-following-up property cannot be obtained. If the melting point ofthe second resin is lower than 130° C., it is feared that the resinwhich gives following-up property at the time of hot press is forcedout.

The first and second resins may be compatible with each other orincompatible with each other.

Combinations of the first and second resins may be the following resins.That is, examples of the first resin having a melting point of 50 to130° C. include an α-olefin such as ethylene, propylene, butene,pentene, hexene, octene, or methylpentene, or copolymers made from twoor more thereof; and copolymers made from one or more α-olefins, such asethylene, and one or more compounds selected from vinyl acetate, acrylicacid, methacrylic acid, acrylic acid ester, methacrylic acid ester,maleic acid, maleic anhydride, norbornene, ethylidenenorbornene andothers. The first resin may be polyethylene resin, ethylene-vinylacetate copolymer, ethylene-acrylate copolymer resin, ethylene-methylacrylate copolymer resin, ethylene-ethyl acrylate copolymer resin,ethylene-butyl acrylate copolymer resin, or the like. Examples of thesecond resin having a melting point higher than 130° C. and not higherthan 250° C. include polypropylene based resin, (1-)butene based resin,polypentene based resin, polymethylpentene based resin, polyesters suchas polybutylene terephthalate, polypropylene terephthalate andpolyethylene terephthalate, polyamides such as 6-nylon (registered trademark), 11-nylon (registered trade mark) and 12-nylon (registered trademark), polycarbonate, and modified compounds thereof.

The blend ratio between the first and second resins is not particularlylimited, and the ratio of the second resin is desirably from 5 to 100parts by weight, more preferably from 10 to 50 parts by weight based on100 parts by weight of the first resin. If the blend ratio of the secondresin is less than 5 parts by weight, the following-up layer may not berestrained from being forced out at the time of hot press. If the ratiois more than 100 parts by weight, the shape-following-up property maybecome low.

Preferably, the lower limit of the complex viscosity of the following-uplayer is 1000 Pa·s at 170° C., and the upper limit thereof is 10000 Pa·sat 170° C. If the viscosity is less than 1000 Pa·s, the resinconstituting the following-up layer may be forced out at the time of hotpress so that the resin may stain the press hot plate or the like. Ifthe viscosity is more than 10000 Pa·s, the thermosetting resin adhesiveagent may not be sufficiently restrained from being forced out from thecover-lay film. More preferably, the lower limit is 3000 Pa·s and theupper limit is 8000 Pa·s.

The lower limit of the complex viscosity of the following-up layer ispreferably 100 Pa·s at 250° C., and the upper limit thereof ispreferably 5000 Pa·s at 250° C. If the viscosity is less than 100 Pa·s,the viscosity is too low so that the moldability may be poor. If theviscosity is more than 5000 Pa·s, at the time of producing the layer bya multi-layer co-extrusion method an interface between the layer and theother layer easily gets rough so that the quality of the externalappearance may be damaged. More preferably, the lower limit is 500 Pa·sand the upper limit is 3000 Pa·s.

The tan δ of the following-up layer is preferably less than 1 at 170° C.If the tan δ is more than 1, the resin constituting the following-uplayer may be forced out at the time of hot press so that the resin maystain the press hot plate or the like. The tan δ is more preferably lessthan 0.9.

The tan δ of the following-up layer is preferably 1.5 or more at 250° C.If the tan δ is less than 1.5, at the time of producing the layer by amulti-layer co-extrusion method an interface between the layer and theother layer easily gets rough so that the quality of the externalappearance may be damaged. More preferably, the tan δ is 1.8 or more.

In the present specification, the complex viscosity and the tan δ meanthose measured by use of a parallel plate of 25 mm diameter as a toolunder conditions of a frequency of 10 rad/second, a strain of 10% andtemperatures of 170° C. and 250° C., and can be measured by use of anRMS-800 manufactured by Rheometric Co., or the like.

Such a following-up layer wherein the complex viscosity and the tan δare compatible with each other is not particularly limited. Theinventors have made eager investigations to find that theabove-mentioned complex viscosity and the tan δ can easily be expressedwhen a resin composition comprising two or more resins is used to formthe following-up layer in such a manner that the two or more resins forma phase separation structure.

The phase separation structure is not particularly limited, and examplesthereof include a co-continuous structure, a sea-island structure, and alayered structure. Of these, the sea-island structure is preferred sincethis structure produces only a small effect on the softening property ofeach of the resins. Particularly preferred is a sea-island structurecomprising at least the first and second resins which are incompatiblewith each other. For the selection of the resins constituting thesea-island structure, it is preferred that the melting point of thesecond resin constituting the islands is higher than that of the firstresin constituting the sea. If the melting point of the second resinconstituting the islands is lower than that of the first resinconstituting the sea, the effect of restraining the resins from beingforced out at the time of hot press may lower.

The first resin constituting the sea of the above-mentioned following-uplayer, which has a sea-island structure, is not particularly limited.The lower limit of the melting point thereof is preferably 50° C., andthe upper limit thereof is preferably 130° C. If the melting point islower than 50° C., the multi-layer sheets are melted and bonded to eachother when they are stored or transported. Consequently, the multi-layersheets may be unpractical. If the melting point is more than 130° C., aneffect of restraining the thermosetting adhesive agent from being forcedout from the cover-lay film may not be obtained. The lower limit is morepreferably 80° C. and the upper limit is more preferably 120° C.

Examples of the resin which can be used as such a resin include anα-olefin such as ethylene, propylene, butene, pentene, hexene, octene,or methylpentene, or copolymers made from two or more thereof; andcopolymers made from one or more α-olefins, such as ethylene, and one ormore compounds selected from vinyl acetate, acrylic acid, methacrylicacid, acrylic acid ester, methacrylic acid ester, maleic acid, maleicanhydride, norbornene, ethylidenenorbornene and others. The resin may bepolyethylene resin, ethylene-vinyl acetate copolymer, ethylene-acrylatecopolymer resin, ethylene-methyl acrylate copolymer resin, ethyleneethyl acrylate copolymer resin, ethylene-butyl acrylate copolymer resin,or the like. These resins may be used alone or in combination of two ormore thereof.

The second resin constituting the islands of the above-mentionedfollowing-up layer, which has a sea-island structure, is notparticularly limited if this resin is a resin incompatible with theresin constituting the sea. The lower limit of the melting point thereofis preferably 130° C. If the melting point is lower than 130° C., aneffect of restraining the following-up layer from being forced out atthe time of hot press may not be obtained. The lower limit is morepreferably 200° C. Example of the second resin having a melting pointhigher than 130° C. and not higher than 250° C. include high-densitypolyethylene, polypropylene and poly(1-)butene. Examples of the resinhaving a melting point of 200° C. or higher include polymethylpentene,polyester resins such as polybutylene terephthalate, polyamides such as1′-nylon (registered trade mark), 12-nylon (registered trade mark) and6-nylon (registered trade mark), polycarbonate, and modified compoundsthereof.

As an example of the combination of these resins, the first resin andthe second resin are low-density polyethylene and polybutyleneterephthalate, respectively, ethylene ethyl acrylate and polybutyleneterephthalate, respectively, or ethylene vinyl acetate copolymer and6-nylon (registered trade mark), respectively.

In the case of the above-mentioned following-up layer having asea-island structure, about the blend ratio between the first resinconstituting the sea and the second resin constituting the islands, theratio of the resin constituting the islands is desirably from 5 to 100parts by weight, more preferably from 10 to 50 parts by weight based on100 parts by weight of the resin constituting the sea. If the blendratio of the resin constituting the islands is less than 5 parts byweight, the resins may not restrained from being forced out at the timeof hot press. If the blend ratio is more than 100 parts by weight, theshape-following-up property may not be sufficient. The multi-layer sheetmay comprises, besides the first and second resins, one or moredifferent resins.

The above-mentioned releasing layer comprises a resin compositionincluding mainly a resin having a melting point of 200° C. or higher. Ifthe melting point of the resin as the main component is lower than 200°C., the layer cannot express heat resistance against hot press so thatthe releasability lowers. Preferably, the melting point is 220° C. orhigher.

In the present invention, the releasing layer and the second releasinglayer which is added at will have the same structure or differentstructures. When the releasing layers of any two out of the multi-layersheets according to the present invention are pressed and bonded ontoeach other under a condition of 170° C. and 3 MPa for 30 minutes, it ispreferred that the releasing layers exhibit a blocking force of 0.1 N/cmor less, the blocking force being measured in accordance with ASTMD1893. If the blocking force is more than 0.1 N/cm, the releasability isinsufficient. Accordingly, in the case of using a process for producinga product wherein a plurality of the multi-layer sheets of the presentinvention are laminated, it may be difficult that the multi-layer sheetsare finally peeled from each other without any compulsion. The blockingforce is more preferably 0.02 N/cm or less.

It is preferred that the resin which constitutes the above-mentionedresin composition, the melting point of the resin being 200° C. orhigher, has a polar group. When the releasing layer comprises the resincomposition including mainly the resin having a polar group, thereleasing layer becomes a layer excellent in mechanical properties. Itis preferred that the resin having a polar group has the polar group inthe main chain thereof. By use of the resin having a polar group in themain chain thereof, the resultant multi-layer sheet of the presentinvention becomes a multi-layer sheet more satisfactory in mechanicalproperties. The wording “having a polar group” in the presentspecification means that an ester, amido, imide, ether, thioether,carbonyl, hydroxyl, amino or carboxyl group or some other groupconstitutes a portion of the resin.

The above-mentioned resin having a polar group is not particularlylimited, and examples thereof include aromatic polyester,polyphenylenesulfide, polyetheretherketone, and aromatic polyamide. Asthe resin having a polar group in the main chain thereof, there ispreferably used at least one resin selected from copolymer of polyesterand α-olefin, copolymer of polymethylpentene and α-olefin, polyester andpolymethylpentene. Of these, crystalline aromatic polyester having acrystalline group in the main chain thereof is preferred for thefollowing reason: when this polyester is subjected to incineratingtreatment, environment load is decreased since the polyester does notcontain any heteroatom in the molecule thereof; therefore, it is alsoeconomically profitable.

The crystalline aromatic polyester can be yielded by causing an aromaticdicarboxylic acid or an ester-producing derivative thereof to react witha low molecular weight aliphatic diol or a high molecular weight diol.Examples of the aromatic dicarboxylic acid or ester-producing derivativethereof include terephthalic acid, isophthalic acid, orthophthalic acid,naphthalenedicarboxylic acid, paraphenylenedicarboxylic acid, dimethylterephthalate, dimethyl isophthalate, dimethyl orthophthalate, dimethylnaphthalenedicarboxylate, and dimethyl paraphenylenedicarboxylate. Thesemay be used alone or in combination of two or more thereof.

Examples of the low molecular weight aliphatic diol include ethyleneglycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol,1,4-butanediol, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, and1,4-cyclohexanedimethanol. These may be used alone or in combination oftwo or more thereof.

Examples of the high molecular weight diol include polyethylene glycol,polypropylene glycol, polytetramethylene glycol, and polyhexamethyleneglycol. These may be used alone or in combination of two or morethereof.

Examples of the crystalline aromatic polyester made from theabove-mentioned components include polyethylene terephthalate,polybutylene terephthalate, polyhexamethylene terephthalate,polyethylene naphthalate, polybutylene naphthalate, and butanediolterephthalate polytetramethylene glycol copolymer. These may be usedalone or in combination of two or more thereof. Of these, aromaticpolyester containing at least butylene terephthalate as a crystallinecomponent is preferred. When the butylene terephthalate component iscontained, the resultant releasing layer is excellent in stainresistance and crystallinity.

The multi-layer sheet of the present invention preferably has a crystalmelting heat quantity of 40 J/g or more. If the quantity is less than 40J/g, the sheet may not express heat resistance against hot pressmolding. Moreover, the dimensional change rate at 170° C. also becomeslarge; accordingly, at the time of hot press molding, the circuitpattern may be damaged. The quantity is more preferably 50 J/g or more.In the case that the crystalline aromatic polyester in the releasinglayer contains a butylene terephthalate component as a crystallinecomponent, the crystal melting heat quantity is more preferably 40 J/gor more.

In order to improve the crystallinity to make the crystal melting heatquantity high, an additive for promoting crystallization, such as acrystal nucleus agent, may be added to the above-mentioned resincomposition. The cooling temperature at the time of melt-molding themulti-layer sheet is set preferably to a temperature not lower than theglass transition temperature of the aromatic polyester, more preferablyto a temperature of 70 to 150° C. The crystal melting heat quantity canbe measured by differential scanning calorimetry (DSC).

The surface of the releasing layer preferably has smoothness. It isallowable to give thereto slipping property, anti-blocking property orthe like necessary for handling. An appropriate embossment pattern maybe given to at least one of the faces thereof in order to remove air attime of hot press molding.

The releasing layer is preferably subjected to heat treatment in orderto improve the heat resistance and the dimensional stability thereof, inparticular, the releasability. In the case of producing the releasinglayer by a melt molding method, at the time when the raw materialsthereof are discharged in a melt state from a T-die and then cooled andfixed with a cooling roll, incomplete crystal, which is not sufficientlycrystallized, may remain on the surface of the releasing layer. Whensuch incomplete crystal is present on the surface of the releasinglayer, it appears that the releasability is poor since surface moleculesin the releasing layer keep high molecular mobility. When the releasinglayer is subjected to heat treatment to crystallize the incompletecrystal, the molecular mobility of the surface molecules in thereleasing layer is suppressed so that the releasability can be improved.

The method for the heat treatment is not particularly limited. Forexample, a method of passing the multi-layer sheet between rolls heatedto a constant treatment temperature is preferred since the multi-layersheet can be treated in steps continuous from the melt molding method.

The temperature for the heat treatment is not particularly limited ifthe temperature is a temperature higher than the glass transitiontemperature of the resin constituting the releasing layer and not higherthan the melting point thereof. The lower limit thereof is preferably120° C. and the upper limit is preferably 200° C. If the temperature islower than 120° C., the releasability-improving effect based on the heattreatment is hardly obtained. If the temperature is higher than 200° C.,the releasing layer deforms easily and thus the layer may not beproduced. The lower limit is more preferably 170° C. and the upper limitis more preferably 190° C.

It is effective for an improvement in the releasability of the releasinglayer to subject the releasing layer to rubbing treatment. By therubbing treatment, the above-mentioned incomplete crystal isrecrystallized by frictional energy so that strong crystal is formed.Therefore, the crystal would suppress the molecular mobility of surfacemolecules in the releasing layer so that the releasability can beimproved.

The method for the above-mentioned rubbing treatment is not particularlylimited, and an example thereof is a method of rubbing the surface ofthe releasing layer with a rotating member such as a metal roll, orcloth such as gauze. The direction of the rubbing in the rubbingtreatment is not particularly limited. The direction may be parallel orperpendicular to the longitudinal direction of the releasing layer. Itis preferred to rub the releasing layer surface at a rate of 30 m/minuteor more by use of, for example, a piece of cloth or a brush.

Since the purpose of the rubbing treatment is the crystallization of theabove-mentioned surface molecules, it is unnecessary to apply suchrubbing that the surface roughness of the releasing layer changes beforeand after the rubbing treatment.

The releasing layer can exhibit very good mechanical properties sincethe layer has the above-mentioned structure. In other words, when tworeleasing layers out of a plurality of the releasing layers are pressedand bonded onto each other under a condition of 170° C. and 3 MPa for 30minutes, the releasing layers exhibit a blocking force of 0.02 N/cm orless, the blocking force being measured in accordance with ASTM D1893.At 170° C., at which hot press is ordinarily performed, the storageelastic modulus is from 20 to 200 MPa, the 100% elongation load is from49 to 490 mN/mm, the tensile fracture elongation is 500% or more, andfurther the dimension change rate is 1.5% or less when the releasinglayer is pressed at a load of 3 MPa and 1700C for 60 minutes. Since suchmechanical properties can be exhibited, the releasing film of thepresent invention is very suitable as a releasing film used in theprocess for producing a printed circuit board, a flexible printedcircuit board or a multi-layer printed circuit board.

If the blocking force measured in accordance with ASTM D1893 when thereleasing layers are pressed and bonded to each other under a conditionof 170° C. and 3 MPa for 30 minutes is more than 0.02 N/cm, thefollowing is caused: when the releasing film of the present invention isused as a releasing film in the process for producing a printed circuitboard, a flexible printed circuit board or a multi-layer printed circuitboard, the peeling resistance when the releasing film is peeled afterhot press becomes large so that workability deteriorate or, in somecase, the circuit is damaged.

As described above, a good reliability can be remarkably expressed, inparticular, when the releasing layer is subjected to heat treatment orrubbing treatment.

When the releasing layer is overlapped with polyimide and/or metal foiland the resultant is pressed at 170° C. and 3 MPa for 60 minutes, thereleasing layer has high reliability from the polyimide and/or metalfoil. The wording “has releasability” means that after the pressingtreatment, the releasing force generated between the polyimide and/ormetal foil and a sheet or film is low and thus the polyimide and/ormetal foil or the sheet or film is/are not broken when the sheet or filmis peeled.

The above-mentioned crystalline aromatic polyester preferably comprisesa polyester having in the main chain thereof a polyether skeleton. Sucha polyester is obtained by causing an aromatic dicarboxylic acid or anester-forming derivative thereof to react with a low molecular weightaliphatic diol and a high molecular weight diol.

About the resin composition containing such a crystalline aromaticpolyester, flexibility can be obtained while heat resistance andreleasability are kept by dispersing a crystalline aromatic polyestercontaining a high molecular weight diol component finely into a matrixcomprising a crystalline aromatic polyester containing no high molecularweight diol.

The above-mentioned polyester, which has in the main chain thereof apolyether skeleton, preferably has a melting point of 170° C. or higher.If the melting point is lower than 170° C., the resultant multi-layersheet may be poor in releasability when the sheet is used as a releasingsheet. Such a polyester having in the main chain thereof a polyetherskeleton is not particularly limited, and examples thereof includebutanediol terephthalate polytetramethylene glycol copolymer andbutanediol terephthalate polypropylene glycol copolymer.

The content of the above-mentioned polyester, which has in the mainchain thereof a polyether skeleton, in the crystalline aromaticpolyester is preferably 50% or less by weight. If the content is morethan 50% by weight, the resultant sheet may not easily be peeled whenthe sheet is used as a releasing sheet.

The halogen content in the resin composition constituting the releasinglayer is preferably 5% or less by weight. According to this, toxicmaterials containing a halogen are not generated even if the multi-layersheet is incinerated. The halogen content is preferably 3% or less byweight, more preferably 1% or less by weight. If the halogen content isless than 1% by weight, the approval of substantial non-halogen materialin Europe can be obtained.

The resin composition constituting the releasing layer may contain astabilizer as long as staining resistance does not become a problem.Examples of the stabilizer include hindered phenol antioxidants such as1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene,3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)-propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane; and thermalstabilizers such as tris(2,4-di-t-butylphenyl)phosphite,trilaurylphosphite, 2-t-butyl-α-(3-t-butyl-4-hydroxyphenyl)-p-cumenylbis(p-nonylphenyl) phosphite, dimyristyl 3,3′-thiodipropionate, distearyl3,3′-thiodipropionate, pentaerystyryltetrakis(3-laurylthiopropionate)and ditridecyl 3,3′-thiodipropionate.

The resin composition constituting the releasing layer may containadditives such as a fiber, an inorganic filler, a flame retardant, anultraviolet absorbent, an antistatic agent, an inorganic material, and ahigher fatty acid salt as long as the practicability is not damaged.

Examples of the fiber include inorganic fibers such as glass fiber,carbon fiber, boron fiber, silicon carbide fiber, alumina fiber,amorphous fiber and silicon/titanium/carbon based fiber; and organicfibers such as aramide fiber. Examples of the inorganic filler includecalcium carbonate, titanium oxide, mica, and talc. Examples of the flameretardant include hexabromocyclododecane,tris-(2,3-dichloropropyl)phosphate, and pentabromophenyl allyl ether.

Examples of the ultraviolet absorbent include p-t-butylphenylsalicylate, 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-methoxy-2′-carboxybenzophenone, and2,4,5-trihydroxybutyrophenone. Examples of the antistatic agent includeN,N-bis(hydroxyethyl)alkylamine, alkylallylsulfonate, andalkylsulfanate. Examples of the inorganic material include bariumsulfate, alumina, and silicon oxide. Examples of the higher fatty acidsalt include sodium stearate, barium stearate and sodium palmitate.

The resin composition constituting the releasing layer may contain athermoplastic resin or a rubber component in order to modify the naturethereof. Examples of the thermoplastic resin include polyolefin,modified polyolefin, polystyrene, polyamide, polycarbonate, polysulfone,and polyester. Examples of the rubber component include natural rubber,styrene-butadiene copolymer, polybutadiene, polyisoprene,acrylonitrile-butadiene copolymer, ethylene-propylene copolymer (EPM orEPDM), butyl rubber, acrylic rubber, silicon rubber, urethane rubber,olefin-based thermoplastic elastomer, styrene-based thermoplasticelastomer, vinyl chloride-based thermoplastic elastomer, ester-basedthermoplastic elastomer, and amide-based thermoplastic elastomer.

The resin composition constituting the releasing layer preferablycontains an inorganic compound having a large aspect ratio. When thecomposition contains the inorganic compound, which has a large aspectratio, the releasability of the multi-layer sheet of the invention athigh temperatures can be improved. Furthermore, the additives or lowmolecular weight components are restrained from being bled out to thesurface, whereby cleanliness can be improved at the time of hot pressmolding.

Examples of the inorganic compound include lamellar silicates such asclay, and lamellar bihydrates such as hydrotalcite.

As illustrated in a schematic, front sectional view as FIG. 1, themulti-layer sheet of the present invention may be a multi-layer sheet 3composed of a releasing layer 1 and a shape following-up layer 2. Asillustrated in a front sectional view as FIG. 2, the multi-layer sheetmay be a multi-layer sheet 5 having a three-layer structure wherein asecond releasing layer 4 is laminated on a face of a following-up layer2 opposite to the following-up layer face on which a releasing layer 1is laminated. The case of the three-layer structure is preferable sinceexcellent following-up property to irregularities of a board surface andexcellent releasability from both faces of the board and a press hotplate can be obtained. The multi-layer sheet of the invention may have alaminated structure having four or more layers, or may have any otherlayer than the following-up layer and the releasing layers.

The lower limit of the thickness of the following-up layer is preferably50 μm, and the upper limit thereof is preferably 300 μm. If thethickness is less than 50 μm, the following-up property toirregularities may become insufficient. If the thickness is more than300 μm, the thermal conductivity at the time of hot press molding maydeteriorate.

The lower limit of the thickness of the releasing layer is preferably 5μm, and the upper limit thereof is preferably 100 μm. If the thicknessis less than 5 μm, sufficient releasability is not expressed. If thethickness is more than 100 μm, the following-up effect based on thefollowing-up layer is hindered by the releasing layer so that asufficient following-up property may not be obtained.

The method for producing the multi-layer sheet of the invention is notparticularly limited. Examples thereof include a method of forming filmsby a water-cooling or air-cooling co-extrusion inflation method or aco-extrusion T-die method; a method of laminating the resin compositionconstituting the following-up layer onto the releasing layer by anextrusion laminating method; and a method of dry-laminating thereleasing layer and the following-up layer which are separatelyprepared. Of these, the method of forming films by a co-extrusion T-diemethod is preferred since the controllability of the thickness of eachof the layers is excellent.

The multi-layer sheet of the invention is excellent in flexibility athigh temperature, heat resistance, releasability and stain resistance.The sheet can easily disposed of at safety, and/or the sheet isexcellent in following-up property to an irregular face and the propertythat constituents thereof are not forced out. Furthermore, the sheet iseasily disposed of after the use thereof. Accordingly, when acopper-clad laminated board or copper foil is hot-pressed through aninterposed prepreg or heat resistant film in the process for producing aprinted circuit board, a flexible printed circuit board, a multi-layerprinted circuit board or the like, the multi-layer sheet of theinvention is used suitably as a releasing sheet for preventing bondingbetween a press hot plate and the printed circuit board, flexibleprinted circuit board, multi-layer printed circuit board or the like.Moreover, when a cover-lay film or cover-lay films is/are bonded througha thermosetting adhesive agent by hot press molding in the process forproducing a flexible printed circuit board, the multi-layer sheet of theinvention is used suitably as a releasing sheet for preventing bondingbetween the cover-lay film and the hot press plate or between thecover-lay films.

According to the present invention, it is possible to provide amulti-layer sheet which is excellent in heat resistance, releasabilityand following-up property to an irregular face, is hardly forced out atthe time of hot press to exhibit excellent stain resistance, and iseasily disposed of after the use thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, front sectional view illustrating an embodimentof the multi-layer sheet of the present invention.

FIG. 2 is a schematic, front sectional view for explaining a multi-layersheet of another embodiment of the invention.

EXPLANATION OF REFERENCE NUMBERS

-   1 . . . releasing layer-   2 . . . following-up layer-   3 . . . multi-layer sheet-   4 . . . releasing layer-   5 . . . multi-layer sheet

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail by way of thefollowing examples. However, the present invention is not limited onlyto the examples.

Example 1

A three-layer co-extruder was used to produce a multi-layer sheet havinga three-layer structure wherein the following three layers werelaminated in order that the layers will be described: a layer, 25 μm inthickness, made of Hytrel 2751 (manufactured by Du Pont-Toray Co., Ltd.,a resin composition comprising mainly a polyester having a halogencontent of 0% by weight and a glass transition temperature of 53° C. anda polyester containing in the main chain thereof ether groups as polargroups); a following-up layer, 100 μm in thickness, made of EMMA (methylmethacrylate resin containing a polar group, trade mark: Acrift WH102,manufactured by Sumitomo Chemical Co., Ltd.); and a layer, 25 μm inthickness, made of the same Hytrel 2751 as described above. Separately,an extruder was used to produce a 100-μm sheet made of the same EMMA asa sheet for evaluating the following-up layer.

Example 2

In the same way as in Example 1, a multi-layer sheet having athree-layer structure was produced, and then the multi-layer sheet waspassed between two rolls, 300 mm in diameter, heated to 175° C. at arate of 10 m/minute, thereby subjecting the sheet to heat treatment toproduce a multi-layer sheet of Example 2.

Example 3

In the same way as in Example 1, a multi-layer sheet having athree-layer structure was produced, and then the sheet was subjected toa rubbing treatment by bringing the sheet into contact with a rollwherein a piece of gauze was wound around the outside surface made ofthe above-mentioned Hytrel 2751, the roll being rotated at a peripheralspeed of 90 m/minute in the direction reversal to the direction in whichthe sheet was carried, thereby yielding a multi-layer sheet of Example3.

Example 4

A multi-layer sheet was yielded in the same way as in Example 2 exceptthat the material of the central following-up layer was changed fromEMMA to a low density polyethylene (abbreviated to LDPE in Table 1.Petrocene 173R, manufactured by Tosoh Corp.).

Example 5

A multi-layer sheet of Example 5 was yielded in the same way as inExample 2 except that the material of the central following-up layer waschanged from EMMA to a composition comprising 70 parts by weight of anethylene-ethyl acrylate copolymer (abbreviated to EEA. Jrex A3100,manufactured by Japan Polyolefins Co., Ltd.) and 30 parts by weight of apolypropylene (article number: PC600S, manufactured by SunAllomer Ltd.).

Example 6

A multi-layer sheet having a three-layer structure was produced whereinthe following three layers were laminated in order that the layers willbe described: a layer, 25 μm in thickness, made of a polybutyleneterephthalate resin (abbreviated to PBT. Novaduran 5040ZS (manufacturedby Mitsubishi Engineering-Plastics Corp.); a layer, 100 μm in thickness,made of 90 parts by weight of a linear low-density polyethylene resin(Affinity PL1880, manufactured by Dow Chemicals Co.) and 10 parts byweight of the same polybutylene terephthalate resin (Novaduran 5040ZS(manufactured by Mitsubishi Engineering-Plastics Corp.); and a layer, 25μm in thickness, made of the same polybutylene terephthalate resin(Novaduran 5040ZS (manufactured by Mitsubishi Engineering-PlasticsCorp.).

Separately, an extruder was used to produce a 100-μm sheet made of 90parts by weight of the same linear low-density polyethylene resin(Affinity PL1880, manufactured by Dow Chemicals Co.) and 10 parts byweight of the same polybutylene terephthalate resin (Novaduran 5040ZS(manufactured by Mitsubishi Engineering Plastics Corp.) as a sheet forevaluation.

Example 7

A three-layer extruder was used to produce a multi-layer sheet having athree-layer structure wherein the following three layers were laminatedin order that the layers will be described: a layer, 25 μm in thickness,made of the above-mentioned polybutylene terephthalate resin (Novaduran5040ZS (manufactured by Mitsubishi Engineering Plastics Corp.); a layer,100 μm in thickness, made of 90 parts by weight of the above-mentionedethylene-ethyl acrylate copolymer (Jrex A3100, manufactured by JapanPolyolefins Co., Ltd.) and 10 parts by weight of the same polybutyleneterephthalate resin (Novaduran 5040ZS (manufactured by MitsubishiEngineering Plastics Corp.); and a layer, 25 μm in thickness, made ofthe same polybutylene terephthalate resin (Novaduran 5040ZS(manufactured by Mitsubishi Engineering Plastics Corp.). Separately, anextruder was used to produce a 100-μm sheet made of 90 parts by weightof the same ethylene-ethyl acrylate copolymer (Jrex A3100, manufacturedby Japan Polyolefins Co., Ltd.) and 10 parts by weight of the samepolybutylene terephthalate resin (Novaduran 5040ZS (manufactured byMitsubishi Engineering Plastics Corp.) as a sheet for evaluation.

Example 8

A three-layer extruder was used to produce a multi-layer sheet having athree-layer structure wherein the following three layers were laminatedin order that the layers will be described: a layer, 25 μm in thickness,made of the above-mentioned polybutylene terephthalate resin (Novaduran5040ZS (manufactured by Mitsubishi Engineering Plastics Corp.); a layer,100 μm in thickness, made of 90 parts by weight of the above-mentionedethylene-ethyl acrylate copolymer (Jrex A3100, manufactured by JapanPolyolefins Co., Ltd.) and 10 parts by weight of a polyester resin(Hytrel 4047, manufactured by Du Pont-Toray Co., Ltd.); and a layer, 25μm in thickness, made of the same polybutylene terephthalate resin(Novaduran 5040ZS (manufactured by Mitsubishi Engineering PlasticsCorp.). Separately, an extruder was used to produce a 100-μm sheet madeof 90 parts by weight of the same ethylene-ethyl acrylate copolymer(Jrex A3100, manufactured by Japan Polyolefins Co., Ltd.) and 10 partsby weight of the same polyester resin (Hytrel 4047, manufactured by DuPont-Toray Co., Ltd.) as a sheet for evaluation.

Example 9

A three-layer extruder was used to produce a multi-layer sheet having athree-layer structure wherein the following three layers were laminatedin order that the layers will be described: a layer, 25 μm in thickness,made of the above-mentioned polybutylene terephthalate resin (Novaduran5040ZS (manufactured by Mitsubishi Engineering Plastics Corp.); a layer,100 μm in thickness, made of 90 parts by weight of a low densitypolyethylene (Petrocene 175R, manufactured by Tosoh Corp.) and 10 partsby weight of the same polybutylene terephthalate resin (Novaduran 5040ZS(manufactured by Mitsubishi Engineering Plastics Corp.); and a layer, 25μm in thickness, made of the same polybutylene terephthalate resin(Novaduran 5040ZS (manufactured by Mitsubishi Engineering PlasticsCorp.).

Separately, an extruder was used to produce a 100-μm sheet made of 90parts by weight of the same low density polyethylene (Petrocene 175R,manufactured by Tosoh Corp.) and 10 parts by weight of the samepolybutylene terephthalate resin (Novaduran 5040ZS (manufactured byMitsubishi Engineering Plastics Corp.) as a sheet for evaluation.

Comparative Example 1

A multi-layer sheet of Comparative Example 1 was produced in the sameway as in Example 1 except that the material of the two outside layerswas rendered a polypropylene (article number: PC600S, manufactured bySunAllomer Ltd.) instead of the Hytrel 2751.

Comparative Example 2

A three-layer extruder was used to produce a multi-layer sheet having athree-layer structure wherein the following three layers were laminatedin order that the layers will be described: a layer, 25 μm in thickness,made of the above-mentioned polybutylene terephthalate resin (Novaduran5040ZS (manufactured by Mitsubishi Engineering Plastics Corp.); a layer,100 μm in thickness, made of the above-mentioned linear low-densitypolyethylene resin (Affinity PL1880) manufactured by Dow Chemicals Co.;and a layer, 25 μm in thickness, made of the same polybutyleneterephthalate resin (Novaduran 5040ZS (manufactured by MitsubishiEngineering Plastics Corp.).

Separately, an extruder was used to produce a 10-μm sheet made of thesame linear low-density polyethylene resin (Affinity PL1880) as a sheetfor evaluation.

Comparative Example 3

A three-layer extruder was used to produce a multi-layer sheet having athree-layer structure wherein the following three layers were laminatedin order that the layers will be described: a layer, 25 μm in thickness,made of the above-mentioned polybutylene terephthalate resin (Novaduran5040ZS (manufactured by Mitsubishi Engineering Plastics Corp.); a layer,100 μm in thickness, made of the above-mentioned ethylene-ethyl acrylatecopolymer (Jrex A3100, manufactured by Japan Polyolefins Co., Ltd.); anda layer, 25 μm in thickness, made of the same polybutylene terephthalateresin (Novaduran 5040ZS (manufactured by Mitsubishi Engineering PlasticsCorp.).

Separately, an extruder was used to produce a 100-μm sheet made of thesame ethylene-ethyl acrylate copolymer (Jrex A3100, manufactured byJapan Polyolefins Co., Ltd.) as a sheet for evaluation.

(Evaluation)

About the multi-layer sheets and the sheets for evaluation yielded inExamples 1-9 and Comparative Examples 1-3, evaluations were made by thefollowing methods. The results are shown in Tables 1-3.

(1) Evaluation of the Blocking Force of Each Releasing Layer

Two sheets of each kind of the multi-layer sheets yielded as describedabove were prepared, and their releasing layers were pressed and bondedto each other under a condition of 170° C. and 3 MPa for 30 minutes, soas to measure the blocking force thereof by a method according to ASTMF1893.

(2) Evaluation of the Dynamic Viscoelasticity of Each Following-UpLayer:

About each of the sheets for evaluation, an RMS-800 manufactured byRheometric Co. or the like was used and a parallel plate of 25 mmdiameter was used as a tool to measure the complex viscosity and the tanδ thereof at 170° C. and 250° C. under a condition of a frequency of 10rad/second, a strain of 10%, a temperature of 120-270° C. and atemperature-raising rate of 5° C./minute.

(3) Evaluation of the Structure of Each Following-Up Layer:

The sheets for evaluation were each frozen with liquid nitrogen, andthen a cross section thereof was prepared with a microtome. Thecross-section was observed with a transmission electron microscope(manufactured by JEOL Ltd.).

(4) Practicability Evaluation:

A polyimide film (Kaptone, manufactured by Du Pont Co.) of 25 μmthickness was used as a base film to produce a copper-clad laminatewherein a copper foil of 35 μm thickness and 50 μm width was bonded ontothe base film through an epoxy adhesive agent layer of 20 μm thickness.Separately, an epoxy adhesive agent having a flow starting temperatureof 80° C. was applied onto the same polyimide film (Kaptone,manufactured by Du Pont Co.) of 25 μm thickness, so as to have athickness of 20 μm. In this way, a cover-lay film was produced.

A product wherein each of the multi-layer sheets, the copper-cladlaminate, the cover-lay film, and the same multi-layer sheet werelaminated in this order was called one set. Thirty two out of aplurality of the sets were put on a hot press. The 32 sets weresubjected to hot-press molding under a condition of a press temperatureof 170° C. and a press pressure of 3 MPa for a press time of 60 minutes,and then the press pressure was cancelled. The multi-layer sheets werepeeled therefrom so as to yield a flexible printed circuit board. In theproduction of this flexible printed circuit board, the releasability,the adhesive property, electrode stains of the produced flexible printedcircuit board, the forcing-out of the following-up layer from themulti-layer sheets, and the adhesion thereof onto the press hot platewere evaluated with the naked eye and an optical microscope (power: 100magnifications). TABLE 1 Releasing Layer Following-Up Layer LayerStructure Ex. 1 Hytrel 2751 EMMA(WH102) 25/100/25 Ex. 2 Hytrel 2751EMMA(WH102) 25/100/25 Ex. 3 Hytrel 2751 EMMA(WH102) 25/100/25 Ex. 4Hytrel 2751 LDPE(173R) 25/100/25 Ex. 5 Hytrel 2751 EEA(70)/PP(30)25/100/25 Ex. 6 PBT PL1880(90)/PBT(10) 25/100/25 Ex. 7 PBTEEA(90)/PBT(10) 25/100/25 Ex. 8 PBT EEA(90)/Hytrel(10) 25/100/25 Ex. 9PBT LDPE(90)/PBT(10) 25/100/25 Comp. PP EMMA(WH102) 25/100/25 Ex. 1Comp. PBT PL1880 25/100/25 Ex. 2 Comp. PBT EEA 25/100/25 Ex. 3

TABLE 2 Following-Up Layer Releasing Layer Complex Blocking Resin ResinViscosity Surface Force Melting Melting (Pa · s) tan δ Treatment (N/cm)Composition Point (° C.) Composition Point (° C.) Phase Structure 170°C. 250° C. 170° C. 250° C. Ex. 1 None 0.04 Polar Group 220 Polar Group90 — 7000 — 0.65 — Contained Contained Ex. 2 Heat 0.015 Polar Group 220Polar Group 90 — 7000 — 0.65 — Treatment Contained Contained Ex. 3Rubbing 0.017 Polar Group 220 Polar Group 90 — 7000 — 0.65 — TreatmentContained Contained Ex. 4 Heat 0.015 Polar Group 220 Nonpolar 110 — 7000— 0.65 — Treatment Contained Ex. 5 Heat 0.015 Polar Group 220 PolarGroup  95 and 165 A Clear 6500 — 0.9 — Treatment Contained ContainedStructure was Unable to be Observed Ex. 6 None 0.03 Polar Group 224Polar Group 100 and 224 Sea-Island 7000 2300 0.85 1.90 ContainedContaining-Resin Structure Blend Ex. 7 None 0.03 Polar Group 224 PolarGroup 104 and 224 Sea-Island 6000 1800 0.88 1.85 Contained ContainedStructure Ex. 8 None 0.03 Polar Group 224 Polar Group 104 and 190Sea-Island 5700 1800 0.95 2.00 Contained Contained Structure Ex. 9 None0.03 Polar Group 224 Polar Group 111 and 224 7500 2800 0.65 1.10Contained Containing-Resin Blend Comp. None — Nonpolar 165 Polar Group90 — 7000 — 0.65 — Ex. 1 Contained Comp. None 0.03 Polar Group 224 PolarGroup 100 — 6500 2200 1.70 2.20 Ex. 2 Contained Containing-Resin BlendComp. None 0.03 Polar Group 224 Polar Group 104 — 3000 1300 1.50 2.10Ex. 3 Contained Contained

TABLE 3 Practicability Evaluation Following-Up Electrode Forcing-Out ofthe Following-Up Layer, Releasability Property Stains and AdhesionThereof onto the Hot Plate Ex. 1 Good Very Good None None Ex. 2 VeryGood Very Good None None Ex. 3 Very Good Very Good None None Ex. 4 VeryGood Good None None Ex. 5 Very Good Very Good None None Ex. 6 Good GoodNone None Ex. 7 Good Good None None Ex. 8 Good Good None The Layer wasSomewhat Forced Out but did not Adhere to the Hot Plate Ex. 9 Good GoodNone None Comp. The Sheet was Melted and was Unpractical Ex. 1 Comp.Good Good None The Layer was Forced Out and Further Ex. 2 the LayerAdhered to the Plate Comp. Good Good None The Layer was Forced Out andFurther Ex. 3 the Layer Adhered to the Plate

1. A multi-layer sheet, which comprises a following-up layer comprisinga resin composition including mainly a resin having a melting point,which is a melting peak temperature measured by DSC, in the range of 50to 130° C., and a releasing layer comprising a resin compositionincluding mainly a resin having a melting point of 200° C. or higher andlaminated on the following-up layer, wherein when the two releasinglayers of the multi-layer sheets are pressed and bonded onto each otherunder a condition of 170° C. and 3 MPa for 30 minutes, the releasinglayers exhibit a blocking force of 0.1 N/cm or less, the blocking forcebeing measured in accordance with ASTM D1893.
 2. The multi-layer sheetaccording to claim 1, wherein when the resin having a melting point inthe range of 50 to 130° C. is called a first resin, the following-uplayer further comprises a second resin having a melting point higherthan 130° C. and not higher than 250° C., the melting point beingmelting peak temperature measured by DSC.
 3. The multi-layer sheetaccording to claim 1, wherein the following-up layer has a complexviscosity of 1000 to 10000 Pa·s at 170° C. and a tan δ of less than 1 at170° C.
 4. The multi-layer sheet according to claim 1, wherein a secondreleasing layer is laminated on a face of the following-up layer whichis opposite to the following-up layer face on which the releasing layeris laminated, the second releasing layer comprises a resin compositionincluding mainly a resin having a melting point of 200° C. or higher,and when the two releasing layers (the first and second releasing layersor the second releasing layers) are pressed and bonded onto each otherunder a condition of 170° C. and 3 MPa for 30 minutes, the releasinglayers exhibit a blocking force of 0.1 N/cm or less, the blocking forcebeing measured in accordance with ASTM D1893.
 5. The multi-layer sheetaccording to claim 1, wherein the following-up layer has a complexviscosity of 100 to 5000 Pa·s at 250° C. and a tan δ of 1.5 or more at250° C.
 6. The multi-layer sheet according to claim 2, wherein thefollowing-up layer has a structure wherein the first and the secondresins are made into a sea-island structure, and the melting point ofthe second resin which constitutes the islands in the sea-islandstructure is higher than that of the first resin which constitutes thesea therein.
 7. The multi-layer sheet according to claim 6, wherein themelting point of the first resin which constitutes the sea is from 50 to130° C.
 8. The multi-layer sheet according to claim 6, wherein themelting point of the second resin which constitutes the islands is 130°C. or higher.
 9. The multi-layer sheet according to claim 1, wherein theresin composition which constitutes the releasing layer is made mainlyof a resin having a polar group in the main chain thereof.
 10. Themulti-layer sheet according to claim 9, wherein the resin having thepolar group in the main chain thereof is a crystalline aromaticpolyester.
 11. The multi-layer sheet according to claim 10, wherein theresin having the polar group in the main chain thereof further comprisesat least one resin of a polymethylpentene and an α-olefin copolymer. 12.The multi-layer sheet according to claim 10, wherein the crystallinearomatic polyester, as the resin having the polar group in the mainchain thereof, comprises at least butylene terephthalate as a crystalcomponent in the releasing layer.
 13. The multi-layer sheet according toclaim 1, wherein the crystal melting heat quantity by DSC is 40 J/g ormore.
 14. The multi-layer sheet according to claim 1, wherein when thetwo releasing layers of the multi-layer sheets are pressed and bondedonto each other under a condition of 170° C. and 3 MPa for 30 minutes,the releasing layers exhibit a blocking force of 0.02 N/cm or less, theblocking force being measured in accordance with ASTM D1893.
 15. Themulti-layer sheet according to claim 9, wherein at least a surface ofthe releasing layer is subjected to heat treatment at a temperaturewhich is not lower than a glass transition temperature of the resinhaving the polar group in the main chain thereof and not higher than themelting point thereof.
 16. The multi-layer sheet according to claim 1,wherein a surface of the releasing layer is subjected to a rubbingtreatment.
 17. The multi-layer sheet according to claim 1, wherein ahalogen content of the releasing layer is 5% by weight or less.